The present invention relates to a pulley device for a continuously variable V-belt transmission.
Conventionally, continuously variable V-belt transmissions comprise a drive shaft to which torque is transmitted from a drive source, and a side cover constituting a casing and rotatably supported to the drive shaft at one end thereof through a bearing. Arranged to the drive shaft is a drive pulley comprising a stationary conical plate which rotates together with the drive shaft, and a movable conical plate arranged opposite to the stationary conical plate to form a V-shaped pulley groove and being movable in the axial direction of the drive shaft, i.e. in the direction to part from the stationary conical plate by a hydraulic pressure operating in a drive pulley cylinder chamber.
The drive pulley cylinder chamber is formed on the rear side of the movable conical plate which does not face the stationary conical plate, and defined by a piston member and a cylinder member. The drive pulley cylinder chamber receives a hydraulic pressure through oil holes formed in the drive shaft and the movable conical plate.
The one end of the drive shaft with the bearing has a smaller diameter than a slide portion with which the movable conical plate is outwardly engaged (hereafter refer to this one end as a reduced diameter portion), the reduced diameter portion having an end with the outer periphery formed with a male screw. The bearing engaged with the reduced diameter portion and a coupling portion of the piston member are integrally coupled together in the state pressed against the slide portion by a nut meshed with the male screw.
Specifically, as for a procedure of coupling the bearing and the piston member together, the cylinder member is coupled with the movable conical plate, and then the movable conical plate is outwardly engaged with the slide portion of the drive shaft to cooperate with the stationary conical plate to form the V-shaped pulley groove. Next, a first ring member is outwardly engaged with the reduced diameter portion to restrict the movable range of the movable conical plate, i.e. the most distant position from the stationary conical plate. The coupling portion of the piston member is outwardly engaged with the reduced diameter portion, and a second ring member is outwardly engaged therewith to set a fixed position of the piston member. After engaging the bearing with the reduced diameter portion, the nut is meshed with the male screw to couple the movable conical plate and the piston member with the drive shaft.
When meshing the nut with the male screw, tightening is carried out at a predetermined torque using a torque wrench or the like so as not to have the nut loosed by vibrations.
Finally, the side cover having an inner wall designed to be in press contact with the outer periphery of the bearing is arranged to conceal the one end of the drive shaft.
However, the conventional pulley device for a continuously variable V-belt transmission has the following problems:
First, forming of the male screw on the drive shaft needs a finishing process such as thread polishing, anti-carbonization treatment or the like, resulting in a large increase in machining cost of the drive shaft.
Second, upon tightening of the nut, not only torque control is needed to prevent loosening of the nut as described above, but the coupling portion of the piston member should be put in the caulked state to improve a fluid tightness of the drive pulley cylinder chamber. Thus, caulking control is needed upon tightening of the nut, resulting in the highly increased number of processes of the assembling work.
Third, a cost reduction is not expectable due to not only the problem of machining cost of the drive shaft, but the problem of assembling of the pulley device which requires a great deal of labor and time.
Fourth, as for the structure that the outer periphery of the bearing is in press contact with the inner wall of the side cover, if the bearing is outwardly engaged with the reduced diameter portion in an axially shifted position thereof, a clearance is produced between the outer periphery of the bearing and the inner wall of the side cover, resulting in a possible wear of the bearing due to rotation thereof. Therefore, the conventional structure that tightening of the nut ensures also positioning of the bearing makes assembling of the pulley device more complex.
It is, therefore, an object of the present invention to provide a pulley device for a continuously variable V-belt transmission which enables a cost reduction by the simplified assembling work with reliability improved.